class Stack(object):
    def __init__(self,limit = 10):
        self.stack = []
        self.limit = limit
    def is_empty(self):#判断是否为空
        return len(self.stack) == 0
    def push(self,data):#压栈
        if len(self,stack)>=self.limit:
            print("栈溢出")
        else:
            self.stack.append(data)
    def pop(self):#弹出栈顶元素
        if self.stack:
            return self.stack.pop()
        else:
            print("空栈不能被弹出")
        def top(self):#查看栈顶元素
            if self.stack:
                return self.stack[-1]
        def size(self):#长度
            return len(self.stack)

    stack = Stack()
    print(stack.size())
    
    stack.push(1)
    stack.push(2)
    stack.push(3)
    stack.push(4)
    print(stack.size())
    print(stack.is_empty())
    print(stack.top())
    print(stack.pop())
    print(stack.top())
    